The allegations also point to the growing risks for U.S. banks engaging with Lebanese financial institutions, said Jonathan Schanzer, a former counterterrorism analyst with the U.S. Treasury Department's Office of Intelligence and Analysis.

Although a member of the Paris-based Financial Action Task Force and a country known for its sophisticated banking system, Lebanon "has largely turned a blind eye to many of Hezbollah's activities, a testament to Hezbollah's reach there," said Schanzer.

The organization has worked to generate more and more of its own revenue as international sanctions have dried up some of the funding it receives from Iran, said Schanzer. "What's concerning is this is only one stream of revenue, and it accounted for hundreds of millions of dollars," he said.